The custodians of the popular cryptocurrency platform Ethereum implemented a controversial change to it Wednesday, but broad questions remain about its long-term impact

The custodians of the popular cryptocurrency platform Ethereum implemented a controversial change to it Wednesday, but broad questions remain about its long-term impact.

The change—called a “hard fork”—was put into place in response to the June theft of $60 million worth of the digital currency. The hard fork essentially undoes the transactions that allowed that theft, thereby allowing the money to be returned its rightful owner....